Tim, let's see if I can save your some money and troubles.. You cannot... use your oem 14" rims for a disc brake conversion because they are NOT disc brake ready rims. You will have to go find a set of disc brake ready rims off a newer Ford disc brake equipped car. I found five on a disc brake equipped Granada at a junk yard and bought them. Now... since you are going to have to buy tires for that Tbird, I would suggest you save yourself some headaches in trying to find disc brake ready 14" rims. Solve the problem by buying 15" rims instead, and 15" tires. Then you wont have the problem. The information on what parts to buy, where to get them the cheapest at, and how to do the disc brake conversion are available to our Paid Members. To become one, have a PayPal account, go to the Donate to Site button at the top of this Forum, and sign up as a Paid Member. There are a lot of additional features, and advantages you get by being a Paid Member. You can find that information in the top section of this Forum in the Announcements section. Paid Membership is $20 a year.
You should also swap out that single MC and the power booster you have under the hood and put in a dual MC and an 8"dual power booster, for safety sake, instead of what you have now. That single MC and booster will not handle a disc brake conversion. We can also tell you what to put on to replace it. I even got my set up in chrome for just $20 over the non-chromed unit. You will be able to detach that booster from the mounting bracket and re-use that bracket since you do not have AC. I would suggest that you invest $20 and become a Paid Member. I think I already gave you $20 in good information!
Here is a pic of what my '59 setup looks like..